The present invention relates to a method for improving utilization of sulphur-absorbent and thus the consumption of sulphur-absorbent when burning sulphur-containing coal in a fluidized bed of particulate material containing material which, upon combustion, combines with sulphur and prevents sulphur oxides from being dispersed into the environment with the fuel gases produced at the combustion. The sulphur-absorbent normally consists of a calcium compound, usually calcium (CaCO.sub.3 ) or dolomite (CaCO.sub.3 . MgCO.sub.3) or a mixture thereof. Hydrated calcium sulphate is a stable compound which can be deposited into the environment without risk of its causing damage.
The invention also relates to a power plant burning coal in a fluidized bed of particulate material in the combustion chamber of a bed vessel. It is particularly intended for power plants in which combustion occurs at a pressure considerably in excess of atmospheric pressure and the combustion gases are used to drive a gas turbine, and where steam is generated to drive a steam turbine.
A number of chemical reactions are obtained at the temperature prevailing in the bed at combustion (800.degree.-950.degree. C.). The absorbent particles are converted partially to calcium oxide (CaO) and sulphated, and a surface layer of hydrated calcium sulphate is formed. Gradually, an absorbent (CaSO.sub.4) and a core of CaCO.sub.3 and/or CaO. The outer layer of calcium sulphate (CaSO.sub.4) impedes the diffusion of sulphur in to the unused absorbent and limits utilization of the absorbent material. In order to improve the level of utilization it is known to remove bed material from the bed and crush the particles so that the calcium sulphate layer is disintegrated and the unconsumed bed material inside the particles is exposed. The crushed bed material is returned to the bed and the unused absorbent material in the bed particles is accessible for absorption of sulphur.